Tuesday, 22 March 2016

Abrupt climate change accepted by scientists

An
influential group of scientists led by James Hansen, the former
NASA scientist often credited with having drawn the first major
attention to climate change in 1988 congressional testimony, has
published a dire climate studythat
suggests the impact of global warming will be quicker and more
catastrophic than generally envisioned.

The
research invokes collapsing ice sheets, violent megastorms and
even the hurling of boulders by giant waves in its quest to suggest
that even 2 degrees Celsius of global warming above pre-industrial
levels would be far too much. Hansen has called it the most important
work he has ever done.

The
sweeping paper, 52 pages in length and with 19 authors, draws on
evidence from ancient climate change or “paleo-climatology,” as
well as climate experiments using computer models and some modern
observations.

“I
think almost everybody who’s really familiar with both paleo and
modern is now very concerned that we are approaching, if we have not
passed, the points at which we have locked in really big changes for
young people and future generations,” Hansen said in an interview.

The
research, appearing
Tuesday in
the open-access journal Atmospheric
Chemistry and Physics, has
had a long and controversial path to life, having first appeared as a
“discussion paper” in the same journal, subject to live, online
peer review — a novel but increasingly influential form of
scientific publishing. Hansen first told the press about the research
last summer, before this process was completed, leading
to criticism from
some journalists and also fellow scientists that he might be jumping
the gun.

What
ensued was a high-profile debate, both because of the dramatic claims
and Hansen’s formidable reputation. And his numerous co-authors,
including Greenland and Antarctic ice experts and a leader of
the United Nations’ Intergovernmental Panel on Climate Change, were
nothing to be sniffed at.

After record
downloads for
the study and an intense
public review process,
a revised version of the paper has now been accepted, according to
both Hansen and Barbara Ferreira, media and communications manager
for the European Geophysical Union, which publishes Atmospheric
Chemistry and Physics.
Indeed, the article is now
freely readable on
the Atmospheric
Chemistry and Physics website.

The
paper, according to Ferreira, was subject to “major revisions
in terms of organisation, title and conclusions.” It also now
has two additional authors.

Most
notably, perhaps, the editorial process led to the removal of
the use of the phrase “highly dangerous,” in the paper’s title,
to describe warming the planet by 2 degrees Celsius above
pre-industrial levels.

The
original paper’s title was “Ice melt, sea level rise and
superstorms: evidence from paleoclimate data, climate modeling, and
modern observations that 2 °C global warming is highly dangerous.”
The final title is “Ice melt, sea level rise and superstorms:
evidence from paleoclimate data, climate modeling, and modern
observations that 2 °C global warming could be dangerous.”

But
nonetheless, James Hansen’s climate catastrophe scenario now takes
its place in the official scientific literature relatively intact. So
let’s rehearse that scenario, again, for the record.

Hansen
and his colleagues think that major melting of Greenland and
Antarctica can not only happen quite fast — leading to as much
as several meters of sea level rise in the space of a century,
depending on how quickly melt rates double — but that this melting
will have dramatic climate
changeconsequences,
beyond merely raising sea levels.

That’s
because, they postulate, melting will cause a “stratification” of
the polar oceans. What this means is that it will trap a pool of
cold, fresh meltwater atop the ocean surface, with a warmer ocean
layer beneath. We have actually seen a possible hint of this with the
anomalously cold “blob” of ocean water off the southern coast of
Greenland, which some have attributed to Greenland’s melting.

Indeed,
shortly before the new paper’s publication, the National Oceanic
and Atmospheric Administration released new
recent data on
the globe’s temperature that certainly bears a resemblance to what
Hansen is talking about. For not only was the globe at a record
warmth overall over the last three months, but it also showed
anomalous cool patches in regions that Hansen suspects are being
caused by ice melt – below Greenland, and also off the tip of the
Antarctic peninsula.

(National
Oceanic and Atmospheric Administration.)

“My
interpretation is that this is the beginning,” Hansen says of these
cool patches in curious parts of the global ocean. “And it’s one
or two decades sooner than in our model.”

However,
when it comes to both the melt rates for Greenland and
Antarctica, and also these cool ocean patches, we have a very limited
time span of observations. It is far from clear, yet, that Hansen’s
interpretation of them will prevail, and the new study also suggests
closely observing these areas in coming years.

Stratification,
the key idea in the new paper, means that warm ocean water would
potentially reach the base of ice sheets that sit below sea level,
melting them from below (and causing more ice melt and thus,
stratification). It also means, in Hansen’s paper, a slowdown or
even eventual shutdown of the overturning circulation in the Atlantic
ocean, due to too much freshening in the North Atlantic off and
around Greenland, and also a weakening of another overturning
circulation in the Southern Ocean.

This,
in turn, causes cooling in the North Atlantic region, even as global
warming creates a warmer equatorial region. This growing north-south
temperature differential, in the study, drives more intense
mid-latitude cyclones, or storms. The study suggests such storms may
kick up gigantic oceanic waves, which may even be capable of feats
such as hurling boulders in some locations, not unlike the huge rocks
seen on the Bahamian island of Eleuthera, which I visited
with Hansen and his co-author,
geologist Paul Hearty, in November.

These
rocks play a key role in the new paper, just as they did in the
original study draft. Indeed, long before the current paper, Hearty
had documented, in peer
reviewed publications,
that Eleuthera’s rocks appear to have come from the ocean and to
have been lifted high up onto a coastal ridge. This appears to have
happened during a past warm period, the Eemian, some 120,000 years
ago, when the planet was only slightly warmer than today but seas
were far higher — but the idea is that something like it could
happen again.

GREGORY
TOWN, BAHAMAS – NOVEMBER 21: The giant boulders of Eleuthera that
have sparked a great debate among scientists about their origin ,
taken on November 21, 2015 in Eleuthera, Bahamas. On the left is ‘The
Bull’ (2000 tons) and on the right is ‘The Cow’ (1000 tons).
Measuring over 20ft in height, the theory put out by Paul Hearty, a
coastal geologist at the University of North Carolina at Wilmington
is that the massive boulders were catapulted onto land by a series of
intense storms. They now sit delicately perched on the coastal ridge
in North Eleuthera. (Photos by Charles Ommanney/The Washington Post)

The
paper contains many ideas and departures, but the key one is its
suggestion of the possibility of greater sea level rise in this
century than forecast by the United Nations’ Intergovernmental
Panel on Climate Change.

“The
models that were run for the IPCC report did not include ice melt,”
Hansen said in a press conference regarding the new paper Monday.
“And we also conclude that most models, ours included, have
excessive small scale mixing, and that tends to limit the effect of
this freshwater lens on the ocean surface from melting of Greenland
and Antarctica.”

There
is a great deal at stake. Hansen has cited the
paper in court proceedings in a case playing out in Oregon, where a
series of young plaintiffs, including his granddaughter Sophie, are
suing the United States for violating their constitutional rights by
allowing fossil fuel burning. While scientists will have to digest
the new version of the paper, when the initial draft paper was
released, at the website of Atmospheric
Chemistry and Physics Discussions,
it prompted both scientific praise and also major skepticism.

David
Archer, a geoscientist at the University of Chicago and a reviewer
for the first round of the paper, called
it “another
Hansen masterwork of scholarly synthesis, modeling virtuosity, and
insight, with profound implications.” But Peter Thorne, another
official reviewer and a climate researcher with the National
University of Ireland Maynooth, wrote
that “it
is far from certain that the results contended shall match what will
happen in the real-world.” Thorne also expressed his “personal
discomfort at the paper being openly and actively publicized before
the discussion period is complete.”

Michael
Mann, a Penn State university climate scientist familiar with the
original study, commented, “Near as I can tell, the issues that
caused me concern originally still remain in the revised
manuscript. Namely, the projected amounts of meltwater seem
unphysically large, and the ocean component of their model
doesn’t resolve key wind-driven current systems (e.g. the Gulf
Stream) which help transport heat poleward. That makes northern
hemisphere temperatures in their study too sensitive to changes in
the Atlantic meridional overturning ocean circulation,” the
scientific name for the ocean circulation in the Atlantic that, the
study suggests, could shut down.

However,
another Penn State researcher, glaciologist Richard Alley, said by
email that “though this is one paper, it usefully reminds us that
large and rapid changes are possible, and it raises important
research questions as to what those changes might mean if they were
to occur. But, the paper does not include enough ice-sheet
physics to tell us how much how rapidly is how likely.”

If
you dig deep enough into the Earth’s climate change archives, you
hear about the Palaeocene-Eocene Thermal Maximum, or PETM. And then
you get scared.

This
is a time period, about 56 million years ago, when something
mysterious happened — there are many ideas as to what — that
suddenly caused concentrations of carbon dioxide in the atmosphere to
spike, far higher than they are right now. The planet proceeded to
warm rapidly, at least in geologic terms, and major die-offs of some
marine organisms followed due to strong acidification of the oceans.